The field of the invention is laboratory evaluation and geo-technical testing of media, in particular an apparatus and methods of its use for evaluation of soft soils or soil slurry materials.
Consolidation testing of soft soil or slurry materials using traditional geo-technical testing methods and equipment is not practically possible, but predicting the consolidation behavior of such materials is of paramount importance in designing for dredged material or mine waste disposal operations, for example. During laboratory self-weight consolidation for modeling the field behavior of media such as dredged or other slurry material, the material undergoes significant strain as pore fluid drains and the media particles compact in the mix. Such strain behavior is modeled differently from that of traditional consolidation behavior. Traditionally, self-weight consolidation is assumed to be negligible and the change in void ratio is assumed to vary directly with the change in the specimen (column) height. Needed is a device and method that overcomes limitations of traditional consolidation testing by allowing self-weight consolidation to freely occur and by enabling determination of void ratio changes directly from tests of the sampled media contained inside each insert in a stack (column).
The only known means of characterizing discrete layer properties of a soft soil material has heretofore been accomplished using a method in which each ring is accessed by moveably sliding an enveloping outer shell in a downward direction. The moveable outer shell has contributed to difficulties in accomplishing accurate specimen testing by unduly disrupting the self-consolidation process, and often impinges on the inner rings.
A preferred embodiment of the present invention enables practical laboratory testing of soft soils and slurries to be accomplished, while validating large strain consolidation theory assumptions.
A consolidometer for determining properties of media, in particular, self-weight consolidation, is provided. As well as solids, the media include fluids incorporating suspended or dissolved solids. It uses inserts that are placed in a stacked configuration in a longitudinal frame, generally set vertically on its base in a containment device. The frame supports the inserts, typically rings, such that any media under investigation is contained wholly within the interior volumes of the inserts, e.g., the annular volume of the stack of ring inserts. The frame may be a cylinder cut in half lengthwise to permit insertion and withdrawal of said ring inserts at locations along its length. Also provided is a collection device, typically a flat tray configured to abut and secure onto any one of the ring inserts and with bosses to fit recesses in the frame. It is used seriatim with the insert rings to collect samples along the length of the media column. The ring inserts are secured to the frame in any of a number of ways, a typical method using one or more set screws for each ring insert. When a sample is taken, the set screws are removed and the ring insert slid out of the stack. Optionally, sensors may be inserted in one or more ring inserts to take additional data on the column of media.
Also provided is a method for determining properties of media, in particular, self-weight consolidation properties. Using a consolidometer that represents a preferred embodiment of the present invention, one fills the stacked inserts of the consolidometer with the media to be evaluated and allows the mediate to self-consolidate. The topmost inserts that no longer contain media are removed. Then, a sample collection device, such as a specially-configured flat tray, is attached to the topmost insert having media contained in its interior volume. The set screws, or other retaining devices, are removed from the insert and the insert is slid from its position on top of the stack out over the flat sample tray. By removing the insert the media contained therein is dropped onto the flat tray for subsequent transfer to a sample vial or like container. The process is then repeated for each insert in the stack. Optionally, one or more of the inserts may be fitted with one or more sensors that provide additional information about the media at that point in the stack, based on a pre-specified data collection protocol.
Advantages of a preferred embodiment of the present invention include:
higher accuracy of laboratory sampling by conducting sampling and testing at discrete spatial intervals;
adaptable to various types of geo-technical test and evaluation;
ease of taking samples with reduced spillage;
multiple laboratory functions able to be provided with a given configuration;
low skill level needed for operators implementing the methods of use;
low cost of the capital equipment needed to implement;
low maintenance cost of the capital equipment; and
low overall cost to implement including cost of necessary supplemental fabrication material.
A preferred embodiment of the present invention overcomes traditional geo-technical testing constraints encountered in laboratory investigations of soft soils or soil slurries because the invention allows for material sampling, material testing, and evaluation of material characteristics during the specimen""s self-weight consolidation process. This enables accurate laboratory representation and modeling of soft soil or slurry self-weight consolidation processes occurring during dredged material disposal, mine tailing operations, or other soft sediment placement scenarios.